Electrolytic cell for producing adiponitrile by electrolytic hydrodimerization of acrylonitrile

ABSTRACT

An electrolytic cell for producing adiponitrile by electrolytic hydrodimerization of acrylonitrile, which comprises one or more sets of an anode plate, a cation exchange membrane and a cathode plate superposed with each other, and at least one duct formed between said anode plate and said membrane and between said cathode plate and said membrane through which electrolyte is passed at a high flowing rate, said duct having at least one turning portion which is positioned outside of an electric current path flowing across the anode and cathode plates.

United States Patent Seko et al. [451 Apr. 18, 1972 [54] ELECTROLYTICCELL FOR 204/269, 275

PRODUCING ADIPONITRILE BY ELECTROLYTIC [56] References CitedHYDRODIMERIZATION OF UNITED STATES PATENTS ACRYLONITRILE 2,708,6585/1955 Rosenberg ..204/257 [72] Inventors: Maomi Seko, Tokyo; AkiraYomiyama, 3,084,113 4/1963 Vallino; ..204/263 Nobeoka; Tetsuya Miyake,Nobeoka; Koji Nakagawa, Nobeoka; Muneo Yoshida, Nobeoka; Koji Inada,Nobeoka, all of Japan Assignee: Asahi Kasei Kogyo Kabushiki Kaisha,

Osaka, Japan Filed: May 1, 1970 Appl. No.: 33,630

Foreign Application Priority Data May 7, 1969 Japan ..44/34499 US. Cl...204/253, 204/73 A, 204/263,

204/269 Int. Cl ..B0lk 3/10 Field of Search ..204/73 A, 245, 253, 257,263,

Primary ExaminerJohn l-l. Mack Assistant Examiner-W. I. SolomonAttorney-Flynn & Frishauf [5 7] ABSTRACT An electrolytic cell forproducing adiponitrile by electrolytic hydrodimerization ofacrylonitrile, which comprises one or more sets of an anode plate, acation exchange membrane and a cathode plate superposed with each other,and at least one duct formed between said anode plate and said membraneand between said cathode plate and said membrane through whichelectrolyte is passed at a high flowing rate, said duct having at leastone turning portion which is positioned outside of an electric currentpath flowing across the anode and cathode plates.

10 Claims, 16 Drawing Figures PATENTEDAPR 18 I972 SHEET 1 BF 5 nu m C!PATENTEDAPR 18 m2 8, 657. 099

SHEET 20F 5 FIG. I d

l6 8 9 IO LL 5 W \1 k u PATENTEDAPR 18 m2 SHEET 3 OF 5 FIG. 3b

PATENTEDAPR 18 I972 SHEET H 0F 5 fi L FIG. 4b

ELECTROLYTIC CELL FOR PRODUCING ADIPONITRILE BY ELECTROLYTICHYDRODIMERIZATION OF ACRYLONITRILE The present invention relates to aconstruction of an electrolytic cell for producing adiponitrile byelectrolytic hydrodimerization of acrylonitrile.

Methods for producing adiponitrile by electrolysis of acrylonitrile havebeen publicly known in the art, as disclosed in Japanese Pat. Nos. 4733/1965 and 11249/1966. Upon con ducting tests we have found that theseconventional methods have some limitations in industrially practicingthe same, as hereinafter described.

When producing adiponitrile by electrolytic hydrodimerization ofacrylonitrile, acrylonitrile and adiponitrile are easily oxidized to belost and hydrogen cyanide gas is produced at the anode area of anelectrolytic cell. Furthermore, gaseous mixtures of oxygen andacrylonitrile produced at the anode area may cause explosion, which isdangerous Accordingly, it is desired to separate anode and cathodechambers by means of a sheet of membrane.

When producing adiponitrile by reduction of acrylonitrile, a surface ofthe cathode becomes alkaline, and at this surface layerbis-cyanoethyl-ether is produced by reaction of acrylonitrile and water.Further hydrolysis products of acrylonitrile and adiponitrile andpropionitrile are produced at this surface layer.

In order to prevent the production of these by-products, it is necessaryto reduce the thickness of the alkaline surface layer formed at thecathode surface to be as thin as possible. For this purpose, it isdesired that flowing rate of catholyte on the cathode surface ismaintained above cm./sec., and preferably above 1 m./sec.

An electrolytic cell having large capacity which can be used in industryis advantageously made in a dual-electrode type construction. Adual-electrode type electrolytic cell includes a plurality of unit cellswhich are superposed with each other and electrically connected inseries, and consequently high voltage can be applied thereto, so thatrectification efficiency is increased, with a transformer having reducedcapacity, which is economical. However, electrolyte is usually fed tothe cells of the respective units separately, so that current leakagemay occur through pipings for feeding the electrolyte. The currentleakage is of course undesirable in itself because it produces loss ofcurrent, and it is particularly undesirable for electrolysis ofacrylonitrile because hydrogen cyanide and the explosive oxygen andacrylonitrile gas mixture may be produced and a part of the piping maybe abnormally corroded since a part of cathode works as an anode becauseof the current leakage. If highly conductive liquid such as sulfuricacid is used as anolyte the current leakage is further increased and adangerous gas mixture of hydrogen and oxygen may be produced.

In order to reduce the current leakage it is necessary to use a finerand longer tube to feed the electrolyte to each unit cell, andconsequently the volume of electrolyte to be fed to each unit cell mustbe minimized.

In order to reduce the flow rate of the electrolyte, it is required toprovide a device for holding the distance between the membrane and theelectrode surface as constant and narrow as possible. It is preferableto provide a tortuous duct for passing the electrolyte on the electrodesurface.

In the hydrodimerization of acrylonitrile, it has been found that ifthere is local stagnation of electrolyte owing to eddy current caused inthe duct, a deposit of polymerized acrylonitrile on the electrodesurface appears, and such deposit increases the eddy current, therebyfurther increasing the deposit. Even if the deposit of polymer may berelatively thin in the order of 0.2 mm. thickness, it acts to reducelargely the feeding rate of acrylonitrile to the electrode surface andincrease the by-product of propionitrile above 5 percent, thus reducingthe yield of adiponitrile. Accordingly, it is required that no obstaclewhich may cause eddy current exists in the passage of the catholyte onthe cathode surface. It is also required that the duct has no abruptlycurved portion therein.

It is preferable that the duct for passing electrolyte on the cathodesurface comprises only straight portions through which the electrolyteuniformly flows.

It is an object of the present invention to provide a novel electrolyticcell for producing adiponitrile by electrolytic hydrodimerization ofacrylonitrile.

It is another object of the present invention to provide an electrolyticcell for producing adiponitrile by electrolytic hydrodimerization ofacrylonitrile which eliminates all of the above-mentioned disadvantages.

The other objects and advantages will be apparent from the descriptionwhich will be made with reference to the accompanying drawings.

Among the known electrolytic cells for producing adiponitrile byelectrolytic hydrodimerization of acrylonitrile, a typical one isdisclosed in Dutch Pat. No. 6,707,472, in which electrolyte flows inpassages which are arranged in the same direction in parallelrelationship and restrictions are provided at inlet and outlet ports ofthese passages to hold the flowing rate uniform through said passages.In such construction, the volume of the electrolyte passing through theunit cell is relatively large, resulting in increase of pressure loss.

An example of the known electrolytic cells including curved ducts isdisclosed in US. Pat. No. 2,708,658. The cell has a curved duct which isarranged between a pair of ion-exchange membranes, instead of beingformed between a membrane and an electrode plate, for the purpose ofdesalting solution, so that this cell has no defect of producing polymereven if electric current is passed through the turning portion of thecurved duct. Thus, in the construction of this US. Patent, the electriccurrent is passed through the turning portions of the duct.

Other electrolytic cells have been known in the art, but any of themcannot solve all of the problems mentioned above. These problems can besolved by the present invention.

In accordance with the present invention, the electrolytic cellcomprises an anode chamber and a cathode chamber separated by amembrane, the cathode chamber providing at least one duct for passingelectrolyte, said at least one duct preferably having a rectangularshape in the cross section and being formed by the electrode, themembrane and a spacer for holding uniform the distance between theelectrode and the membrane, with no obstacle being formed in said duct.The duct has a width of 0.5 to 50 cm. in the direction of flow therein.The duct has at least one turning portion so that the entire length ofthe duct in the perpendicular direction of flow is made longer than thelength of one side of the electrode, and electric current is appliedonly on the straight portions of the duct.

Further, in accordance with the present invention the electrolytic cellis a dual-electrode type cell in which a duct for passing electrolytecomprises straight portions situated on the cathode surface and turningportions around the periphery of the electrode, so that electric currentdoes not pass through the turning portions. Such arrangement providesthe entire length of the passage of electrolyte on the electrode surfacewhich is substantially longer than the length of one side of theelectrode. By this construction, the electrolyte on the cathode surfacecan be held at high flowing rate, while the volume of the electrolytefed to the cell is relatively small.

Various electrolysis methods, such as using homogeneous solution oremulsion, have been known in the art. The present invention can beapplied to any of the methods.

Although the membrane may be made of any material which can preventacrylonitrile and adiponitrile from diffusing into the anode chamber andhas high conductivity, a cationexchange membrane is preferred. Asulphonic type cationexchange membrane based on styrene-divinyl benzeneis superior in chemical stability and mechanical strength, and can beused in a reinforced form with any reinforcement such as glass fiber ora homogeneous form having no reinforcement. Preferably, the membranehaving thickness of 0.5 to 2 mm. is used to prevent the diffusion ofacrylonitrile or other material and to provide necessary mechanicalstrength.

The cathode may be made from lead, lead alloy, cadmium, zinc, carbon orthe like. More particularly, lead-antimony, lead-silver, lead-antimonyor like alloys which can be also used as anode material may beadvantageously used in the dual-electrode type cell since such materialcan be used as an anode at one side and as a cathode at the other side.

The anode may be made from lead peroxide, lead, lead alloy such aslead-antimony, lead-silver, lead-antimony-silver or ferrous oxide,carbon, platinum or the like.

The anolyte is preferably an acidic solution, particularly, sulfuricacid solution, where lead alloy which is superior in corrosion resistantproperty is used as the anode material.

In a dual-electrode type cell, an electrode acts as an anode at one sideand a cathode at the other side, so that the electrode can be made as asingle piece when the same material is used as the anode and cathode.When the material of the anode and that of the cathode are differentfrom each other, the anode and cathode plates are connected together toform a dual-electrode.

In order to form the turning portions of the duct at the outside of theelectrode plate, an electrode frame of insulating material may beprovided, which has an anode plate and a cathode plate attached to theopposite sides of said frame and electrically connected together by arod passing through the frame.

Preferably a spacer may be provided to hold the cathode plate and themembrane at uniform distance. If the distance between the cathode plateand the membrane is extremely small, there is a danger of these partscoming into contact with each other, while if the distance is extremelylarge the required voltage is increased and the required volume of flowis also increased. The desired distance is between 0.5 and mm.

To form an electrolyte path on the cathode surface which is straight andhas no obstacle, the spacer contacting with the cathode surface is madein the form of a straight strip arranged in parallel relationship. Thestrip has practically 2 to 20 mm. width. If the distance between thestrips is too great, the membrane may come into contact with theelectrode, while if the distance is to little, the pressure loss isexcessively increased. Therefore, the preferable distance is 0.5 to 50cm.

The duct is formed between the strips which serves as spacers positionedbetween the cathode plate and the membrane. The catholyte flows in theduct as a straight flow.

The length of one side of the electrode is about 20 cm. to 2 m., inindustrial equipment. In the construction according to the presentinvention, the flow of the electrolyte has at least one turning portionso as to make the entire length of the duct longer than the length ofsaid one side of the electrode, and the turning portion is positioned atthe outside of the cathode plate, so as to prevent electric current frompassing through the turning portion. The turning portion may be providedwithin the thickness of the spacer, or it may be carved in the electrodeframe outside the periphery of the electrode plate. In the latter case,it is essential to form the duct in such shape that the eddy currentproduced in the turning portion exerts substantially no effect over theflow in the straight portions.

The turning portions and the straight portions may be connectedsuccessively so as to form a single duct, but pressure loss may beexcessively increased in a large scale electrolytic cell. In such acase, two or more sets of ducts may be provided.

The feeding pressure of the electrolyte should be maintained belowkg./cm. at the inlet side.

The anode chamber is preferably made in the similar construction withthat of the cathode chamber. If the both constructions are identical,the pressure losses in these chambers are equal when the flowing ratesare maintained at the same value, so that the differential pressureacting on the membrane becomes null.

It is desired to minimize the differential pressure across the membraneso that the membrane having decreased mechanical strength and increasedelectrical conductivity can be used. The differential pressure should bebelow 1 kg./cm. preferably below 0.3 kg./cm.

The anode chamber requires less accuracy than the cathode chamber, sothat a reinforcing porous plate or screen may be set in the anodechamber at the side of the membrane for the purpose of facilitating thedischarge of gas or sludge produced in the anode chamber.

The electrolyte can be fed into the anode and cathode chambers throughnoales provided around the electrode frame. The respective nozzles areconnected to conduits having sufficiently long distance and sufficientlysmall diameter to maintain the current leakage outside of the cell tolow value, and the electrolyte is fed through a header thereto. Thecurrent leakage is preferably maintained at 5 percent or less.

In another construction, conduits may be formed in the peripheralportions of superposed unit cells, and slits may be formed to connectsaid conduits to the ducts on the cathode and anode surfaces, wherebythe catholyte and anolyte can be fed. In order to reduce the currentleakage the slits should be as long and fine as possible.

The spacer, the electrode frame and the conduits may be made from anymaterial which is electrically insulating and corrosion-resistant to thecatholyte and anolyte, such as polypropylene, rubber, heat-resistantvinyl-chloride, vinylchloride or the like.

The accompanying drawings illustrate several embodiments of the presentinvention, in which:

FIGS. 1a, 1b, 1c and 1d illustrate a first embodiment of the presentinvention, FIG. 1a being an exploded perspective view of theelectrolytic cell, FIG. 1b being an exploded perspective view of one setof components of the cell, namely electrode plates, spacers and amembrane, FIG. 1c being front views of these components and FIG. 1dbeing an enlarged sectional view of the set of the components;

FIGS. 20, 2b and 2c illustrate a second embodiment of the presentinvention, FIG. 20 being an exploded perspective view of one set ofcomponents of the electrolytic cell, FIG. 2b being front views of thesecomponents and FIG. 2c being an enlarged sectional view of the set ofthe components;

FIGS. 3a, 3b and 3c illustrate a third embodiment of the presentinvention, FIG. 3a being an exploded perspective view of one set ofcomponents of the electrolytic cell, FIG. 3b being front views of thecomponents and FIG. 30 being an enlarged sectional view of the set ofthe components;

FIGS. 4a, 4b and 4 c illustrate a fourth embodiment of the presentinvention, FIG. 4a being an exploded perspective view of one set ofcomponents of the cell, FIG. 4b being front views of the components andFIG. 40 being an enlarged sectional view of the set of the components;and

FIGS. 5a, 5b and 5c illustrate a fifth embodiment of the presentinvention, FIG. 5a being an exploded perspective view of a set ofcomponents of the cell, FIG. 5b being front views of the components andFIG. 5c being an enlarged sectional view of the set of the components.

Now the invention will be explained, with reference to the drawings.FIGS. la, 1b, 1c and 1d illustrate a first embodiment of the invention.Referring to FIGS. 1a and lb, the electrolytic cell includes electrodeframes 1, spacers 2 and cationexchange membranes 3. Referring to FIGS.10 and 1d, the frame 1 comprises a board 8 of insulating material andelectrode plates 9 fitted in both sides of said board 8 in flushtherewith. The electrode plates 9 are electrically connected together bya conductive rod 10 passing through the board 8. The electrode frame 1has feeding and discharging nozzles 16 at its periphery, through whichtunnel-like feeding and discharging ports 11 and 12 extend to thesurface of the electrode. The spacer 2 is made of a thin plate ofinsulating material having substantially the same size as the frame 1and having a cut-out portion 20 therein to form a duct 19. When theframes 1, the spacers 2 and the cation exchange membrane 3 aresuperposed successively, the respective cut-out portions are enclosedbetween the electrodes and the membrane to form the duct 19 for theelectrolyte.

The duct 19 forms essentially one flowing path which leads from thefeeding port 11 to the discharging port 12 and includes at least oneturning portion, the length of said path being substantially longer thanthat of one side of said electrode frame. When the electrode frame 1 andthe spacer 2 are superposed with each other, the turning portions areformed at the outside of the electrode plate 9, so that electrolysisoccurs only in the straight portions of the duct 19. Although the widthand the thickness of the duct 19 depend on the conditions of theelectrolysis and the property of the cation exchange membrane, the widthwithin the range from 0.5 to 50 cm. and the thickness within the rangefrom 0.5 to 5 mm. are employed in practical use. The thickness of theduct 19 is substantially equal to that of the insulating plate 18 usedfor the spacer 2,

The electrolytic cell is fabricated from the above components, as willbe described below. First of all, a pair of press heads 6 are put with asubstantial space therebetween and a pair of anode and cathode frames 4and 5 respectively are put inside of said press heads 6, as shown inFIG. 1a. Each of the anode and cathode frames 4 and 5 respectively hasan electrode plate 9 fitted in one side thereof. Then, the spacers 2,the cation-exchange membranes 3, the spacers 2 and the electrode frames1 are put in this order successively and they are pressed together bymeans of the press heads 6 to form the electrolytic cell. Although oneelectrolytic cell may include two to several hundred electrode frames toobtain desired capacity, it is preferable in practical use that the onecell includes less than two hundred electrode frames.

The above electrolytic cell can be used to perform the electrolytichydrodimerization of acrylonitrile, as follows.

Direct current is applied across the anode and cathode frames 4 and 5,respectively while the catholyte and the anolyte are being fed to acathode chamber 22 formed by the duct 19 enclosed between thecation-exchange membrane and the cathode, and an anode chamber 23adjoining to said cathode chamber, respectively. The electrode plates 9fitted in the electrode frame 1 forms a cathode when it confronts theanode frame 4, while it forms an anode when it confronts the cathodeframe 5. In the above construction of the electrolytic cell, noobstruction is formed in the duct 19 and there is no restriction thereinas in the electrolytic cell disclosed in Dutch Pat. No. 6,707,472, sothat any kind of electrolyte can be used. There is no stagnation of gasor accumulation of precipitate on the electrode surface owing to theelectrolyte flowing on the electrode surface at high flowing rate, above10 cm./sec. and preferably above 1 m./sec. Therefore, the electrolyticcell can be used in horizontal position as shown in FIG. 1, verticalposition or inclined position at any angle,

The distribution of the electrolyte to the electrolytic cell can be madeby headers for the anolyte and the catholyte through flexible tubesleading to the respective electrode frames. In order to prevent thecurrent leakage, the flexible tubes must be as long and small in crosssection as possible. In the construction according to the invention, theflexible tubes can be made sufiiciently long in length and small indiameter to reduce the current leakage to negligible value, since thevolume of the electrolyte flowing one electrode chamber is substantiallysmall.

FIGS. 2 and 3 illustrate modified forms of the electrolytic cellaccording to the present invention.

FIG. 2 illustrates a construction which is substantially similar to thatshown in FIG. 1, except that portions corresponding to the turningportions of the duct 19 in the spacer 2 shown in FIG. 1 are formed bygrooves 14 carved in an electrode frame 1 and a spacer 2 is formed in ashape of a ladder as shown in FIG. 21).

FIG. 3 illustrates another construction in which a portion correspondingto the spacer 2 is formed as an integral part of an electrode frame 1,and consequently an electrolytic cell is constituted from twocomponents, namely, electrode frames 1 and cation-exchange membranes 3.Electrolyte passing through a duct 19 flows into a groove 14 formed inthe frame at the end of said duct, where it reverses its flowingdirection and then flows into a next duct 19. Thus, the electrolyte fedto a feeding port 11 at one end of the electrode frame flows through anessentially single duct having at least one turning portion and it isdischarged through a discharging port 12.

In the construction of the electrolytic cell as shown in FIGS. 1, 2 and3, the width of the duct 19 depends mainly on the surface area of theelectrode and the entire length of the duct as required. If thecation-exchange membrane 3 has not sufficient strength to maintain therequired width of the duct, one or more fine strips 21 are provided inthe duct to prevent the deformation of the membrane. The strip used forsuch purpose may be made of fine insulating material having the samethickness as that of the spacer 2 and width of 3 to 20 mm., andpositioned in parallel with the flowing direction.

FIGS. 4 and 5 illustrate other forms of the electrolytic cell accordingto the present invention, which are somewhat different from those shownin FIGS. 1 to 3.

FIG. 4 shows a construction in which an electrode frame 1 is formed of asingle electrode plate 9 having feeding and discharging conduits 15 atits peripheral portion. The electrode plate forms an anode at its oneside surface and a cathode at its other side surface when current isapplied thereto. A spacer 2 used in this construction is made of a thinplate having a cut portion 20 to form a duct 19 having at least oneturning portion, which is substantially identical with that shown inFIG. 1, and said spacer has conduits 15 as shown in FIG. 4b. In thisconstruction, a shield plate 7 having a central opening and feeding anddischarging conduits 15 at its peripheral portion is positioned betweenthe spacer 2 and the electrode plate 9, so that the turning portions ofthe duct 19 are shielded from direct current applied to the cell. Theshield plate 7 is made of a thin insulating plate having a thickness of0.05 to 0.2 mm.

The electrolytic cell is fabricated by setting a pair of press heads 6,putting an anode plate 4 and a cathode plate 5 inside of said pressheads, in the same manner as shown in FIG. 1, then putting the shieldplate 7, the spacer 2, the cationexchange membrane 3, the spacer 2, theshield plate 7 and the electrode plate repeatedly in this order betweensaid anode and cathode plates and pressing these parts together by saidpress heads. The electrolyte is fed to the respective chambers of thecell through the feeding and discharging conduits 15 and the nozzles 16extending through the press heads 6. The feeding and dischargingconduits extending through the electrode plates 9 must be completelysealed by means of seals 17 at the area contacting with the electrolytepassing through the conduits, in order to prevent the electrolyte fromcontacting with the electrode plates, which may cause electrolysis.

FIG. 5 illustrates another form of the electrolytic cell according tothe present invention, which is a modified form of FIG. 4. In the formshown in FIG. 5, an electrode frame 1 made from insulating material hasa central opening, into which an electrode plate 9 having the samethickness as that of the electrode frame is fixed. The electrolytic cellincludes spacers 2 and cation-exchange membranes 3 which are identicalwith those shown in FIG. 4. The electrode plate 9 has such dimensions asto sufficiently cover only straight portions of a duct 19 to preventcurrent from flowing through turning portions of the duct. The electrodeplate is formed as an integral piece which acts as an anode at one sideand a cathode at the other side. The electrode plate 1 has conduits 15at its peripheral portion, as shown in FIG. 5b, through whichelectrolyte is fed to the respective chambers.

It will be understood from the above description that a shield plate 7such as shown in FIG. 4 is not required in this construction. Therefore,the electrolytic cell includes three components, namely, the electrodeframes 1, the spacers 2 and the cation-exchange membranes 3, which arerepeatedly superposed with each other to form a cell having any desiredcapacity. Although a single electrolytic cell can be formed from two toseveral hundred electrode plates, it is preferably made from less thantwo hundred plates in practical use.

Now, the invention will be explained with reference to typical examples.

EXAMPLE 1 The electrolytic cell as shown in FIG. 3 has been operatedunder the following conditions.

Electrode frame Material: polypropylene Size: 1,300 X 1,300 X 20 mm.

Electrode plate (anode & cathode) Material: hard lead Size: 1,220 X1,140 X 4 mm.

Spacer Material: polypropylene Size: 1,300 X 1,300 X 2 mm.

Passage: Width-40 mm.

Entire length-27.30 m. Number-24 Current passing area-109 dm.

Cation-exchange membrane Material: sulphonate type strong acidic ionexchange membrane based on butadiene copolymer Size: 1,280 X 1,280 X 1.2mm.

Catholyte Material: aqueous solution containing acrylonitrile andtetraalkyl ammonium salt as supporting salt Flowing rate: 600l./hr./chamber Anolyte Material: 2N aqueous solution of sulphuric acidFlowing rate: 550 l./hr./chamber Number of chambers 40 pairs Current2,200 amp.

After the electrolytic cell was operated for about 1,000 hours under theabove conditions, adiponitrile was produced in the catholyte at the rateof 145 kg. (average)/hour. The pressure drop of the catholyte in thecell was 2.8 kg./cm. while the pressure drop of the anolyte was 2.9kg./cm. The variation of the flowing rate between the respectivechambers was below 3 percent, and consequently extremely uniformdistribution of the flowing rate was obtained. After operation, noaccumulation of precipitate was found in the electrolytic cell.

EXAMPLE 2 The electrolytic cell and the conditions of operation inExample l were modified as follows:

Spacer Size: 1,300 X 1,300 X 2 mm.

Passage: Width- 140 mm.

Entire length-9.12 m.

Number-8 Two strips each having width of 10 mm. and length of 1,140 mm.were inserted in one duct.

Current passing area-109 dm.

Catholyte Flowing rate: 1.7 M /hr./chamber Anolyte Flowing rate: 1.6 M/hr./chamber Number of chambers 10 pairs Current 2,200 amp.

After the cell was operated for about 400 hours under the aboveconditions, adiponitrile was produced at the rate of 48 k g.(average)/hour. After operation, no accumulation of precipitate was found in thecell.

EXAMPLE 3 The electrolytic cell as shown in FIG. 5 was operated underthe following conditions.

Electrode frame Outer frame Material: polypropylene Outside size: 1,000X 1,000 X 6 mm. Inside size: 820 X 810 mm.

Electrode plate Size: 838 X 828 X 6 mm. Conduits Number: 1 for feedinganolyte l for discharging anolyte 1 for feeding catholyte l fordischarging catholyte Size: 80 X 30 mm.

The outer frame and the electrode plate were connected by stepped joint,with packing material inserted therein to prevent leakage.

Spacer Material: polypropylene Size: 1,000 X 1,000 X 2 mm.

Passage: Width-25 mm.

Number-22 Entire length17.8 In. Current passing areaea-44 clm.

When the electrode frame and the spacer were superposed as shown in FIG.5, the turning portions of the duct were positioned at the peripheralportion of the electrode frame. Thus current passes only through thestraight portions of the duct.

Cation-exchange membrane Material: same as Example 1.

Size: 980 X 980 X 1 mm.

Catholyte Material: same as Example 1.

Flowing rate: 380 l./hr./chamber Anolyte Material: same as Example 1.

Flowing rate: 350 l./hr./chamber Number of chambers 20 pairs Current 900Amp.

After the cell was operated for about 300 hours under the aboveconditions, adiponitrile was produced at the rate of 31kg.(average)/hour. After operation, no accumulation of precipitate wasfound in the electrolytic cell.

When the above electrolytic cell was operated for about 300 hours whileapplying current across the turning portions of the duct, the yield ofadiponitrile was lowered and the volume of by-product, such aspropionitrile and biscyanoethyl-ether was increased. After theoperation, accumulation on the cathode of 780 mg.(average) per chamberwas found around the turning portions.

Average yields of material when current was passed across the turningportions and those when no current was passed were as follows.

Current passing across turning portions 1. An electrolytic cell forproducing adiponitrile by electrolytic hydrodimerization ofacrylonitrile, comprising at least one set of an anode plate, a cathodeplate and a membrane superposed between said anode and cathode plates,and at least one duct formed between said membrane and said cathodeplate, said at least one duct having at least one turning portiontherein to form a substantially longer path for flowing electrolyte thanthe length of one side of said plate, said turning portion beingpositioned outside of the path of the current applied across said anodeand cathode plates.

2. An electrolytic cell according to claim 1, in which said membrane isa cation-exchange membrane.

3. An electrolytic cell according to claim 1, in which the distancebetween said cathode plate and said membrane is 0.5 to 5 mm.

4. An electrolytic cell according to claim 1, in which said at least oneduct has straight portions arranged in parallel relationship.

5. An electrolytic cell according to claim 1, in which said at least oneduct has a width between 2 mm. and 20 mm.

6. An electrolytic cell according to claim 1, in which the turningportions are formed in peripheral portions of the cathode plate outsideof the path of the current applied across said anode and cathode plates.

7. An electrolytic cell according to claim 6, in which the turningportions of said at least one duct are in the shape of grooves.

8. An electrolytic cell according to claim 1, in which at least one ductis formed by a spacer having a cut-out portion, said spacer beingpositioned between said membrane and said

2. An electrolytic cell according to claim 1, in which said membrane isa cation-exchange membrane.
 3. An electrolytic cell according to claim1, in which the distance between said cathode plate and said membrane is0.5 to 5 mm.
 4. An electrolytic cell according to claim 1, in which saidat least one duct has straight portions arranged in parallelrelationship.
 5. An electrolytic cell according to claim 1, in whichsaid at least one duct has a width between 2 mm. and 20 mm.
 6. Anelectrolytic cell according to claim 1, in which the turning portionsare formed in peripheral portions of the cathode plate outside of thepath of the current applied across said anode and cathode plates.
 7. Anelectrolytic cell according to claim 6, in which the turning portions ofsaid at least one duct are in the shape of grooves.
 8. An electrolyticcell according to claim 1, in which at least one duct is formed by aspacer having a cut-out portion, said spacer being positioned betweensaid membrane and said cathode plate.
 9. An electrolytic cell accordingto claim 8, in which the turning portions of said at least one duct areprovided within the thickness of the spacer.
 10. An electrolytic cellaccording to claim 1, in which a reinforcing porous plate is provided atthe anode side on said membrane.